Art of cracking hydrocarbons



Jan. 30, 1934. E. w. ISOM ART OF CRACKING HYDROCARBONS Filed April 12. 1929 I\NVENTOR EdWardJ/(ffam Patented Jan. '30, 1934 UNITED STATES,

ART OF CRACKING HYDROCARBONS Edward w. Isom, Scarsdale, N. '1., assignor to Sinclair Refining Company, New York, N. Y.,

a corporation of Maine Application April 12, 1929. Serial No. 354,45o

2 Claims. (01. 196- 58) This 'nvention relates to improvements in the cracking of higher boiling hydrocarbon oils such as gas oil to produce therefrom lower boiling hydrocarbon oils such as gasoline. This appli- 6 cation, in certain aspects, relates to improvements in the method of operation described in an application filed May 26, 1928, Serial No. 283,021. In carrying out the invention, as in the method of operation described in the application menl tioned above, oil, gas oil for example, is forced successively through primary and secondary stages in a heating zone under superatmospheric pressure and thence into an expansion chamber maintained under a pressure lower than that prevailing in the heating zone and from which vapors are taken of! and residue is discharged, the oil is heated to a high cracking temperature in the primary stage in the heating zone, a relatively cool oil is introduced into the oil passing $0 from the primary to the secondary stage in the heating zone lowering the oil temperature and the oil mixture is discharged from the secondary stage in the heating zone at a temperature lower than that at which the oil is discharged from 2 the primary stage in the heating zone. The high boiling oil supplied to the primary stage in the heating zone is thus subjected to severe cracking conditions and to maintained cracking conditions while over-cracking is avoided by limiting .the time at which this oil is at the extreme high temperature. The secondary stage in the heatin zone may be sub-divided and relatively cool oil introduced at a number of points through the secondary stage. The high boiling oil is with advantage preheated, for example, to an incipient cracking temperature, before introduction into the primary stage in the heating zone. This preheating may be accomplished, for example, by heat exchange with heating gases escaping from the major heating operations.

The vapors taken of! from the expansion chamber may be condensed in toto to form a composite product which may then be fractionated in any convenient manner for the separation of a gasoline product, a gas oil fraction or fractions and any higher boiling fraction or fractions; These vapors, however, with advantage are subjected to direct fractionation for the separation of such several fractions.

In carrying out the present invention, however, instead of introducing a relatively low boiling relatively refractory cool oil into the oil passing from the primary to the secondary stage in the heating zone, as in the method of operation described in the application mentioned above, a

relatively high boiling oil which need not be refractory and which may include residual components, crude oil or reduced crude oil for example, is introduced into the oil passing from the primary to the secondary stage in the heating 50 zone lowering the oil temperature and the oil mixture is discharged from the secondary stage in the heating zone at a temperature lower than that at which the oil is discharged from the primary stage in the heating zone. Such relatively high boiling oil, crude oil stock for example, maythus be utilized to control the crack-. ing of the lower boiling raw oil and at the same time be subjected to a preliminary relatively mild cracking operation and to an operation for the separation of a fraction or fractions suitable to be supplied to the primary stage in the heating zone. Using less refractory oil, an increased amount of the relatively high boiling oil maybe introduced into the oil passing from the primary 7 to the secondary stage in the heating zone.

The invention will be further described in connection with the accompanying drawing which illustrates one form of apparatus adapted for carrying out the invention. It will be understood that the accompanying drawing is largely diagrammatic and conventional; the apparatus is shown generally in elevation partly in section and with parts broken away.

The heating furnace illustrated comprises a series of heating flues in which are arranged banks of heating tubes connected to form three single continuous coils, a firebox and a stack flue, all connected so that the heating gases from the firebox 1 pass successively through'the heating flues 2, 3 and 4 to the stack flue 5. Ducts, including suitable forcing means, are provided to permit recirculation of a part of the heating gases escaping from flue 3 to flue 4 through flues 2 and 3'as shown at 6 and to permit recirculation of a part of the heating gases escaping through the stack flue 5 through flues 3' and 4 as shown at '1.

In canying out the invention in the apparatus illustrated, high boiling oil is forced by means of pump 8 through preheating coil 9, cracking coil 1 10 and cracking coil 11 in succession and'then into expansion chamber 12 through pressure regulating and reducing valve 13. Residual oil or tar is discharged from expansion chamber 12 through line 14. Vapors are discharged from expansion chamber 12 through line 15 into the lower end of fractionating tower 16. The fractionating tower 16 may be of any conventional type, for example it may be a so-called "bubble tower. The

fractionating tower 16 and the expansion chamno her 12 are with advantage thoroughly lagged or thermally insulated. In the fractionatlng tower those components of the vapor mixture heavier than suitable as components of the desired product are condensed. This condensation may be eflected by circulating all or a part of the oil supplied to the'secondary stage in the heating zone through cooling coil 17 in the upper end of tower 16 or by the reintroduction into the upper end of tower 16 of part of the distillate product through line 18 by means of pump 19 or by both of these means. Vapors remaining uncondensed escape from the upper end of tower 16 through line 20 to condenser'21 arranged to discharge into receiver 22. The condensed product is discharged from receiver 22 through connections 23 and 24 and uncondensed vapors and gases through connection 25. A high boiling fraction may be recirculated through the cracking coils 10 and 11 .in admixture with raw gas oil. The highest boiling fraction separated in tower 16, for example, may be supplied, or in part supplied, to the preheating coil 9 directly or through the cooler 30 from the lower end of tower 16 through lines 26 and 27. All or part of this fraction may be discharged through connection 29, the oil fraction in this event usually being passed through the cooler 30. An intermediate fraction or fractions may be withdrawn from the fractionating tower 16 through line 34 and discharged, through cooler 33 if necessary, through connection 28 or through connection 29.

The high boiling oil or oil mixture supplied thereto is heated to a high cracking temperature in the cracking coil 10, the primary stage. As this hot oil passes from the cracking coil .10 to the cracking coil 11, a crude oil or a reduced crude oil, for example, is introduced through line 31 by means of pump 32.

The following example of conditions of operation useful in carrying out the invention for the production of gasoline from gas oil and reduced crude oil will illustrate the invention. The discharge pressure from the heating coil 11 may be in the neighborhood of 400-700 pounds per square inch. Pressure in the expansion chamber 12 may approximate atmospheric pressure, or the expansion chamber may be operated under superatmospheric pressures, for example 20-25 pounds per square inch, lower, however, than the discharge pressure from the heating coil 11. Fractionating tower 16 may be operated under substantially the same pressure as the expansion chamber 12- or, when the expansion chamber 12 is operated under superatmospheric pressure, the fractionating tower 16 may be operated under a pressure lower than that prevailing in the expansion'chamber 12.v Raw gas oil supplied through connection 35 may enter the preheating coil 9 through connection 36 at a temperature approximating 60-80 F., although this temperature may exceed 300 F.' if a condensate fraction separated in tower 16 is supplied to the preheating coil 9 in admixture with such raw gas oil. Oil passing from the preheating coil 9 to theheating coil 10 may be at a temperature approximating 550-750 F. The oil may be heated in the heating coil 10 to a temperature, as discharged, approximating 900-950 F. Reduced crude oil introduced into the hot oil passing from the heating coil 10 to the heating coil 11 may be supplied through connec tion 31 at a temperature in the range of 60-350 F., and the resulting oil mixture may enter the heating coil 11 in the neighborhood of 650-750" F. This oil mixture may be heated in the heating coil 11.to a temperature, as discharged, approximating 750-950 F. When the fractionating toward 16 is operated under substantially atmospheric pressure, the temperature of the escaping vapors may be in the neighborhood of 350400 F. It will be understood that the foregoing temperatures and pressures are given to assist in the illustration of the invention and that the invention is not limited thereto.

I claim:

1. In cracking higher boiling hydrocarbon oil to produce gasoline character products, the improvement which comprises forcing high boiling oil successively through primary and secondary stages in a heating zone under super-atmospheric pressure and thence into an expansion chamber, heating the oil in the primary stageto a high cracking temperature as discharged therefrom, introducing a cool higher boiling oil at a temperature less than about 350 F. into the oil passing from the primary stage to the secondary'stage of the heating zone, controlling the amount of cool higher'boiling oil so introduced to reduce the temperature of the hot cracked oil as discharged from the primary stage to a temperature below that at which substantial cracking will take place, further heating the oil mixture so produced in the secondary stage to a cracking temperature lower than the temperature of the oil discharged from the primary stage, reducing the pressure on the oil passing from the secondary stage of the heating zone to the expansion chamber, taking off vapors including vapors of the gasoline character product from the expansion chamber and discharging residue from the expansion chamber.

2. In cracking higher boiling hydrocarbon oil to produce gasoline character products, the improvement which comprises forcing a gas oil successively through primary and secondary stages in a heating zone under superatmospheric pressure and thence into an expansion chamber, heating. the oil in the primary stage to a high cracking temperature as discharged therefrom, introducing a cool crude oil at a temperature less than about 350 F. into the oil passing from the primary stage to the secondary stage of the heating zone, controlling the amount of cool crude oil so introduced to reduce the temperature of the hot 

